1. Field
The present specification relates to an RF frontend module that conducts mobile communication, and to a mobile wireless device equipped therewith.
2. Description of the Related Art
With conventional mobile communication formats implementing FDD (Frequency Division Duplexing), which simultaneously transmits and receives by dividing the frequency region in use into transmit and receive portions, the uplink (UL) frequency band and the downlink (DL) frequency band are locked as a pair. RF frontends utilized for FDD are disclosed in PTL 1 and 2. Examples of such conventional mobile communication formats include UMTS (Universal Mobile Telecommunications System) and FDD-LTE (Frequency-Division Duplexing-Long Term Evolution).
FIG. 1 illustrates examples for three paired frequency bands (pair bands) B1, B3, and B4 as examples of pair bands for FDD. Each pair band is a combination of a transmit (Tx) frequency band corresponding to uplink, and a receive (Rx) frequency band corresponding to downlink.
Meanwhile, a technology called carrier aggregation (CA) has been introduced since LTE-Advanced. Carrier aggregation is a technology that attempts to combine multiple frequency carriers to improve bandwidth and communication speed. This technology includes inter-band carrier aggregation, a form of operation in which a transmit (Tx) frequency band and a receive (Rx) frequency band constituting one of the pair bands illustrated in FIG. 1 are combined with another frequency band, for example.
Combining multiple frequency bands in this way not only enables a wider frequency band to be procured, but also makes asymmetric UL/DL operation possible by bundling distant or isolated frequency bands together, and has the advantage of enabling effective frequency band utilization.
FIG. 2 illustrates an exemplary configuration of an existing RF frontend module compatible with inter-band carrier aggregation.
The RF frontend module 50, disposed between an antenna 101 and an RF transceiver 200, is a unit that performs actions such as filtering out-of-band RF signals and selecting a filter. Internally, the RF frontend module 50 includes a switch unit 10, a diplexer 20, and duplexers 31 to 34 (DUP#1 to DUP#4). The switch unit 10 includes RF switches 11 to 13.
The RF switch 11 is disposed between the diplexer 20 and the antenna 101, and is switched on/off to connect or break the path therebetween. The RF switch 12 is disposed between the duplexer 33 and the antenna 101, and is switched on/off to connect or break the path therebetween. The RF switch 13 is disposed between the duplexer 34 and the antenna 101, and is switched on/off to connect or break the path therebetween.
The diplexer 20 functions to split the frequency band in use between both the duplexer 31 and the duplexer 32.
Since transmitting and receiving are conducted simultaneously with FDD, each of the duplexers 31 to 34 function to provide isolation between the transmit (Tx) frequency band and the receive (Rx) frequency band in a pair so that the transmit (Tx) signal and the receive (Rx) signal do not interfere with each other. As illustrated in FIG. 3, the duplexer 31, for example, is composed of a band-pass filter 312 that selectively passes signals in the transmit (Tx) frequency band, a band-pass filter 313 that selectively passes signals in the receive (Rx) frequency band, and a phase circuit (phase shifter) 311 connected in series to the band-pass filter 313. The phase circuit 311 is configured (designed) with matching circuit and line length settings such that the relationship between the frequency characteristics of the filters is appropriate. Thus, transmit signals or other unwanted signals do not enter the receiving end and good separation between transmit and receive signals is achieved. The matching circuit typically may be composed of inductors and/or capacitors.
Returning to FIG. 2, the RF transceiver 200 includes power amps 211 to 214 respectively connected to the duplexers 31 to 34. The input terminals of the power amps 211 to 214 are the respective transmit ports #1 to #4 of an existing transmitter circuit (not illustrated) inside the RF transceiver 200. The RF transceiver 200 also includes receive ports #1 to #4 respectively connected to the duplexers 31 to 34. Connected to the receive ports #1 to #4 is an existing receiver circuit (not illustrated) that includes low-noise amplifiers (LNAs) 221 to 224.
FIG. 4 is a graph for explaining duplexer operation. The horizontal axis of the graph represents frequency (MHz), while the vertical axis represents attenuation (dB). The waveform Wt illustrates frequency characteristics that indicate how a signal proceeding from a transmit port to an antenna terminal attenuates in a duplexer, while the waveform Wr expresses frequency characteristics that indicate how a signal proceeding from an antenna terminal to a receive port attenuates in a duplexer.
The area A1 portion of the waveform Wt indicates low insertion loss in the transmit frequency band, and indicates that the transmit power efficiency is good. The area A2 portion of the waveform Wr indicates low insertion loss in the receive frequency band, and indicates that the receive sensitivity is good.
Also, the area A3 portion of the waveform Wr indicates that the looping of transmit signals from the duplexer to the receiving end is suppressed, and that receive sensitivity loss due to transmit signals is suppressed. Similarly, the area A4 portion of the waveform Wt indicates that the duplexer is suppressing losses in receive sensitivity due to noise originating from a power amp entering the receiving end.
In the case of utilizing a single band pair (one transmit frequency band and one receive frequency band) given the configuration in FIG. 2, the switch 12 leading to the duplexer #3 connected to the transmit port #3 and the receive port #3 is switched on while the other switches are switched off, for example. Alternatively, the switch 13 leading to the duplexer #4 connected to the transmit port #4 and the receive port #4 is switched on while the other switches are switched off.
In the case of operating inter-band carrier aggregation with two downlinks (2DL) and one uplink (1UL) given the configuration in FIG. 2, the switch 11 leading to the diplexer 20 is switched on while the other switches are switched off. At this point, the transmit port #1 is utilized for transmitting while the receive ports #1 and #2 are utilized for receiving, for example.